I recently found out that the default hop utilization doesnt take into account wort gravity and upon changing to tinseth method found that the estimated IBU's correlated much better with the beers ive been brewing. So I've started doing things a little differently

Since my boil is limited by my 15L pot I've started making up 12 or so litres of lower gravity wort and boiling with my hops to get better utilisation and then adding the rest of the extract in the last 15 minutes or so and bringing it back to the boil to dissolve and sterilise it

and now for the whole point of this post... i think it would be useful if you allowed extracts to have an associated time (like hops) so that you could easily get results for a situation where you go X minutes of high utilisation (lower gravity) then added more extract in the last Y minutes bring the gravity up to finish off. would this be overly hard to add? it looks like the framework is all in place already but perhaps im overlooking a stack of hidden problems with the idea.

on further though, if the late addition of extract made calculating bitterness unwieldy i think just an option to add it "post boil" would do the trick. at the moment ive been unticking the late additions to find approx bitterness and then reticking to find out approx SG.